Experts believe that the disease itself causes heart problems, regardless of the effects of cancer treatments such as chemotherapy, which are known to be toxic to the heart.

Researchers said some cancer patients may need closer monitoring and treatment to reduce the damage to their hearts before, during and after cancer treatment.

The study, from the Royal Brompton Hospital in London, was presented at the EuroEcho-Imaging 2015 conference in Seville.

Experts examined heart function in patients with cancer who had not undergone treatment and compared them with patients with cancer who had had treatment, and a healthy group of patients who were cancer-free.

They looked at subtle measures of heart function - known as heart strain - to detect signs that heart muscle fibres were not contracting as well as they should.

The study found that all 79 cancer patients were showing signs of reduced heart function compared to the healthy control group of 20 patients.

And even those patients with untreated cancer (36 patients) showed very similar levels of heart trouble as those who had undergone cancer treatment (43 patients).

Dr Rajdeep Khattar, consultant cardiologist at Royal Brompton Hospital and one of the lead researchers of the study, said: "Our findings raise the possibility that cancer itself - and not just the drugs used to treat it - may have an adverse impact on heart function.

"Although a relatively small scale study, the results show that more research is now needed to further investigate this link.

"If proven, it could change the way cancer patients are cared for in the future with regards to protecting their heart health.

"At the moment, cancer patients don't routinely have a cardiovascular risk assessment from a cardiologist.

"Our findings could demonstrate a need for that to change because those with reduced strain may benefit from closer monitoring of their heart function."

Professor Peter Johnson, Cancer Research UK's chief clinician, said: "This is a small study and more research is needed to see if there might be a link between cancer and how well the heart works.

"Cancer can have all sorts of effects on the body and it's important this is taken into account when treating patients.

"And this is why it is vital that cancer services are available within hospitals and other clinical centres, where the many different aspects of patients' health and illness can be considered."